1. Field of the Invention
The present invention relates to a noise reduction transmitter which can secure clarity of voices collected in very noisy environments and maintain a quality of sounds.
2. Description of the Related Art
A close-talking microphone is used in order to collect voices in a comparatively noisy environment. As examples of this close-talking microphone, a first-order pressure gradient (unidirectional) microphone unit or two first-order pressure gradient type microphone units to be a second-order pressure gradient microphone are also proposed, however there is a limit on practical use in a noisier environment.
Then, a throat microphone is proposed which takes up vibrations in the throat by means of a piezoelectric device etc. in a noisier environment. According to this throat microphone, in order to detect only vibrations of the throat, a fricative, a plosive sound, etc. which are generated at the mouth cannot be collected. For this reason, it is difficult to secure clarity of voices.
On the other hand, a “Headset Transceiver with Microphone Cover” having a function to collect sound waves generated at a mouth in very noisy environments is disclosed in a product catalog “Headset Transceiver GJH-103 with Microphone Cover” from Kanda Tsushin Kogyo Co., Ltd.
Further, although use is different from this “Headset Transceiver with Microphone Cover”, a transmission device, in which a noise insulation cover is attached to a microphone in order to apply a voice to the microphone without leaking to its surroundings, is disclosed in Japanese Patent Application Publication (KOKAI) No. H5-207116, Japanese Patent Application Publication (KOKAI) No. H9-307614, and a product catalog “Sound Isolation Microphone Mute VMM-150” from MediaCom Japan Inc.
Incidentally, the voice is uttered simultaneously with exhalation through a mouth. Therefore, it is necessary to provide an opening (vent) for discharging exhalation through a noise insulation cover in a structure where the microphone is arranged in the noise insulation cover as disclosed in Japanese Patent Application Publication (KOKAI) No. H5-207116, Japanese Patent Application Publication (KOKAI) No. H9-307614, and the product catalog “Headset Transceiver GJH-103 with Microphone Cover” from Kanda Tsushin Kogyo Co., Ltd., the product catalog “Sound Isolation Microphone Mute VMM-150” from MediaCom Japan Inc.
On the other hand, in the case where the opening for discharging exhalation is provided in the noise insulation cover, noises enter into the noise insulation cover through the above-mentioned opening, so that a sound signal collected by the microphone is influenced by the above-mentioned noise.
Then, a long sound tube (for example) may be attached to the above-mentioned opening provided in the noise insulation cover for discharging exhalation, an air room which prevents a loud noise from entering may be provided, etc., to thereby prevent the noise from entering into the noise insulation cover. However, the whole noise insulation cover including peripherals, such as the above-mentioned sound tube, the air room, etc. increases in size, which is not practical.